Balanceable network electric measuring system



Sept. 21, 1954 J HQRNFECK 2,689,932

BALANCEABLE NETWORK ELECTRIC MEASURING SYSTEM Original Filed Aug. 2, 1947 2 Sheets-Sheet l m N n: m ,5 'IL LU g g llg LIJ h 5 cu 5 2 2 LL I 81' g s; .5 8

INVENTOR.

ANTHONY J. HORN FECK BY ATTOR P 1954 A. J. HORNFECK 2,689,932

BALANCEABLE NETWORK ELECTRIC MEASURING SYSTEM Original Filed Aug. 2, 1947 2 Sheets-Sheet 2 llllllllllll'lllllll MPLIFIEIR INVENTOR.

ANTHONY J. HORNFECK BY Patented Sept. 21,1954

assign I BALANCEABLE NETWORK ELECTRIC MEASURING SYSTEM Anthony J. Hor'nfeck, South Euclid, Ohio, as-

signor to Bailey Meter Company, a corporation of Delaware Original application Au 765,760, new latent teinber 30, 195.2. Divided gust 2, 1947, Serial No.

No. 2,612,628, dated Sep- April 3, 1952, Serial No.

7 Claims. 1

My invention relates to electric measuring systems which are responsive to one or more variable conditions and operate to measure the variable or some function of the variables.

The measurement of a variable condition is frequently accomplished by effecting an unbalance of a balanoeable network in accordance with variations in the condition and causing means to operate as a result of such unbalance and return the network to a balanced condition. It is necessary with such a system to provide leads from the balanced network having resistances so designed as to subject the operating means only to voltages proportional to the actual unbalance oi the network. When the changes of the variable condition are such as to effect only a very sli ht unbalance of the network, it is difficult to produce a change in a resistance of the network to return the latter to a balanced condition. Instead of rebalancing the network, it has been found that better results may be obtained by subjecting the output voltage of the network to an opposing voltage which is regulated by means operating in response to the difference between the two voltages. A close ad.- justment of the opposing voltage may be obtained because substantial operation of the operating means can be made to produce only slight changes in voltage. The resistances of the leads from the network with such an arrangement do not affect the operation of the system. This arrangement does require, however, that the voltage applied to the network for energizing the latter, and voltage applied to the system for producing the opposing voltage, be maintained directly proportional to each other. the system is to operate on direct current, separate sources of power must be provided for the network and the opposing voltage, and regulators are then required to maintain the desired voltage relationship. By operating the system on alternating current, the input voltage for the network and the opposing voltage may be obtained from the same source if a transformer is used in transmitting power to at least one portion of the system so that the separately energized parts are insulated from each other. Any changes in the voltage at the source will then be reflected proportionately to both ends of the network.

If desired, the input voltage to the network may be varied in accordance while the network balance is varied in accordance with one or more variables. Regulation of the voltage opposing the output of the network is then an indication of some function of the variables. By varying the output of one network in response to changes in one or more with one variable and this application variables and opposing this output by a voltage which is caused to vary in response to other variables, as well as by means operating on a difference between the voltages, indications may be obtained of other functions of the variables.

An object of my invention is to provide improved systems for measuring variables. Another object is to provide an improved measuring system in which the voltage output of a network responsive to one or more variables is opposed by a voltage regulated by means operating in response to differences between the voltages. Yet another object is to provide an improved measuring system having means for producing opposing voltages varying in response to variables and brought into balance with each other by means operating in response to differences between the voltages. Other objects will appear in the course or the following description.

In the accompanying drawings there are shown for purposes of illustration several forms which my invention may assume in practice.

In these drawings:

Fig. 1 is a schematic diagram of a system including a bridge circuit which is unbalanced in response to a variable and has its output voltage opposed by another voltage regulated by means operating in response to the differences between the voltages.

Fig. 2 is similar to Fig. 1 but has means for varying the input to the bridge in response to a variable while the bridge unbalance is determined by two variables.

Fig. 3 shows two bridge circuits unbalanced in response to variables and operating together to determine a voltage which is to be measured.

Figs. 4 and 5 show systems in which voltages produced as a result of the unbalance of separate bridge circuits are opposed to each other in determining the operation of means for regulating one of the voltages.

Fig. 6 shows a system in which the output voltage of a bridge unbalanced by a variable condidition is opposed by the output voltage of another bridge which is adjustable to balance the system.

Referring to the drawings it will be noted that there is shown in Fig. 1 a system which is adapted to measure changes in a single variable condition. This system includes a Wheatstcne bridge I having an element 2 forming one of its legs and varying in resistance in response to changes in the condition, a fixed resistance 3 forming a second leg, and fixed resistances i .and 5 combined with portions of the potentiometer 5 to form the third and fourth legs. A contact l is adjustable manually to divide the potentiometer resistance between the third and fourth 3 legs so that the point from which changes are to be measured may be varied at i will. The contact 'lis connected by aconductor 8 to one end of the primary winding of a transformer 9, and the other end of the primary winding is connected to a contact ID of a potentiometer] l. One end of the potentiometer II is connected by a conductor I2 to a point on the bridge between the resistances 2 and 3. A transformer [4 has a primary winding I5 connected to a source of alternating current, and a pair of secondary windings l6, I1, the winding being connected to diagonally opposite pointsofthe bridge for energizing the latter, and thewinding l'l being connected with an adjustable resistance l8 across the potentiometer l I. The secondary winding of the transformer 9 is connected to an amplifier and motor control device which effects operation of a motor 2| in. one-direction or the other depending upon the phase of the voltage energizing the transformer.

The connection of the secondary winding 11 to the potentiometer l i is such that'the voltage drop inv the potentiometer opposes the voltage output of the bridge in determining the flow of current through the primary winding of the transformer 9. When the bridge output exceeds the voltage drop in the portion of the potentiometer between the contact In and the conductor l2, the current flow through the. primary winding of the transformer 9 is such as to effect operationof the motor 2| in a direction to position the contact If) through .a connection 22 so as to increase the portion of the potentiometer connected in the output circuit of the bridge; changes so that the bridge output drops below the opposing voltage from the potentiometer, the motor operates in .a direction to reduce the portion of the potentiometer connected in the bridge output circuit. An indicator 23 is operatively connected to the motorforindicating on a scale the value of'the condition.

In Fig, 2 there .is shown a bridge 26 similar to that of Fig. l but having resistances 21; .28 forming different bridge legs and varying in resistance in response to changes in temperature at different points in a conduit 29 conducting fluid, such as steam. For energizing the bridge there is provided a transformer. having a primary winding flflconnected to a source of alternating current, and a pair of bucking secondary windings 3|; 32 connected. to diagonally opposite points of'the bridge; A core member 34'is supported by a float 35 for movement between the primary and'secondary. windings, and pressures at opposite sides of an orifice 36 in the conduit 29 are suppliedthrough conduits 31, 381to opposite surfaces of the float for determining the position of the latter ina sealing liquid within a container. 39. The float shown herein is so shaped that the position of the core member 34 is changed in response to changes in the rate of fluid flow. The output conductors 8 and 12 of the bridge are shown in this case connected with the variable portion of the potentiometer I l directly to the input terminals of the ampliher and motor control device. The potentiometer II is energized by its direct connection to the source of alternating current through conductors 40 and 41.

When the core member :34 is centered with respect to the secondary, windings 31, 32, the voltage input to the bridge is zero, and thisposition of the core member is-obtained when there is no flow of fluid in the conduit 29. As the core mem- If the condition 1 4 her is moved from its centered position, the voltage induced inone of the secondary windings is increased while it'is decreased in the other winding, and the changes in the induced voltages are in direct proportion to the distance that the core -member-moves. The voltage E1 across the secondary terminals and applied to the input terminals of the bridge is then directly proportional to the rateof fluid flow. Representing the flow of thefiuid by the letter Q, the following equation holds:

where K1=a constant.

Thcunbalance of the bridge is equal to the difference between the resistances 21, 28, and the values of these resistances are directly proportional to the temperatures at the points where the resistances are located. The voltage output of the bridge is proportional to the voltage input times the bridge unbalance. If the temperatures at the resistances 21, 28, are represented by T1 andTz, then the voltage output E2 of the bridge is indicated by the following equations:

where Kd=a constantv In-Fig. 3 there is shown .a system in which a voltage determined by the unbalance of two bridge circuits is opposed by the voltage drop across a portion of the potentiometer II. In this-case; bridge circuits 45, 46 are each provided with fixed resistances in three of itslegs and a resistance forming the fourth leg varying in value-in response to changes in some condition. The values of the variable resistances in bridges 45, 4Bare each representative of a condition and have been indicated by X and K1 respectively. The secondary windings, 49 of a transformer areconnected to diagonally opposite points of the bridge circuits'for energizing thelatter, and athird secondary winding 50 is connected with an adjustable resistance 5| across the potentiometer II; A primary winding 52 is common to the three secondary windings and is connected to a-source of alternating current. Connected across the bridge-circuits at points between the connections to the secondary windings potentiometers-54, having adjustable contacts 56. 515' The-contact 56Kisshown connected to one end of the potentiometer resistance 55 while the contact 511sconnected to one end of the potentiometer-resistance H; One end of the potentiometer54 and the contact I!) are connected to the amplifier 20 by conductors 59 and 60, respectively. Unbalances of thebridge circuits 45, 46- result in voltage .drops across the potentiometers 54', 55; and the output voltages of the bridges are dependentupon the unbalance as well as the positions-of thecontacts 56 51. These contacts areadjusted manually to predetermined positions and then left'in such positions. The voltage outputsofthe-bridges represented by E and El vary; directly in proportion to the changes in the condition, as shown by the equations:

where K and K1 are constants.

With the bridges connected into the system as shown; the; voltage outputs add to oppose the voltage E2. across an adjustable portion of the potentiometer. II. Any voltage difference between the voltage E2. and the sum of E and E1 causes the motor 2| to operate and position the contact it through the connection 22 until E2 equals the total of E and E1. The position of the contact in is then representative of the total of the conditions X and X1 since E2 when the system is balanced is equal to K2 (X+X1) Where K2 is a constant. By reversing the connections from the contact 56 and the end of the potentiometer at, E2 will be representative of the difference between X and X1.

Fig. 4 shows a system in which two bridge circuits M, 65 have their output voltages opposed to each other in determining the operation of the motor 2|. Each of the bridges has one leg varying in resistance in response to changes in a variable, the resistances or variables being indicated by X and X1. The input to bridge 64 is determined by the ositioning of a contact 66 on a potentiometer 61 by a device, such as a Bourdon tube 68, responsive to some variable condition, such as temperature or pressure. The input to bridge 65 is varied in a similar manner by a Bourdon tube 69 operating in response to a variable for positioning a contact along a potentiometer "H. The potentiometers 61 and H are energized by secondary windings l2, 13 of a transformer having its primary winding 14 connected to a source of power. The voltage outputs of the bridges 64, 65 are applied to potentiometers I5, 16 which are connected at one end by a conductor H and have their adjustable contacts H3, '79 connected to the amplifier 20 controlling the operation of the motor 2!. Operative connections 22 between the motor and the contact 18 determine the position of the latter.

The voltages applied to the bridges 64, 65 are representative of the positions of contacts 66, ll) which in turn are representative of the variables acting on the devices 68, 69. These variables may be designated by the letters S and S1, respectively. The voltage output of the bridge at is then equal to KSX while the output of bridge 65 is K1S1X1. The voltage drop in the portion of the potentiometer 76 between the contact iii and the conductor 71 opposes the voltage dro in the portion of the potentiometer between the contact 18 and the conductor 11. The difference between these voltages causes the motor to operate and position the contact 78 until the voltages are equal. contact 18 is representative of a measured value which may be indicated by the letter Y, and the contact 19 may be positioned manually to obtain from the potentiometer 16 a fixed or a variable voltage which may be indicated by the letter Y1. When the voltage input to the amplifier is zero, the following equations apply:

Fig. 5 shows a system similar to that of Fig. i with the unbalance of the bridge 64 determined by a resistance 82 which is varied by a device, such as a Bourdon tube 83, operating in response to changes in a condition, such as pressure in a conduit dd, and the unbalance of the bridge 65 determined by a resistance 85 varying in response to temperature at some point in the conduit. The input to the bridge 64 is determined by the posi- The position of the tioning of a core member 86 relative to bucking secondary windings Bl, 88 of a transformer in response to differentials in pressure at opposite sides of an orifice 39 arranged in the conduit. The voltage output of the bridge 64 is opposed to that of bridge 6-5 to determine the voltage applied to the amplifier 20, and the motor 2! positions the core member 90 relative to bucking secondary windings 9!, 92 to determine the voltage input to bridge 65. The output voltage of each bridge is proportional to its input voltage times its unbalance. The input voltage to bridge 64 is proportional to the pressure differentials across the orifice 89 and may be represented by the letter B. The input voltage to bridge 65 is representative of the positions of the core member 90, and this value may be represented by the letter Z. The unbalances of bridges 64, 65 are proportional to the pressure P and the temperature T, respectively, in the conduit 64. The output voltages of the bridges 64, 65 may then be represented by the equations When the output voltages are equal and the system is balanced, then K 1H P=K2Z T Assuming K1 :K2

HP Z T and is shown by the indicator 23.

Bridge circuits are frequently provided with re sistances forming difierent legs and varying in value with respect to each other on changes in a condition to be measured. In Fig. 6 I have shown a bridge including resistance elements X in two of its legs and resistance elements X1 in the other two legs. The elements X are adapted to change in resistance equal amounts in one direction while the elements X change equal amounts in the opposite direction with changes in a condition to be measured. A bridge similar to this is used in some of the gages available for measur ing strain. This bridge does not include means which is adjustable for varying the point from which the measurements of the condition may be obtained. In order that the point from which measurements are made may be adjusted and that measurements of the values from such point may be obtained, there are provided conductors 96, ill from the output terminals of the bridge to movable contacts 98, 99 of potentiometers we, [Bl connected at their ends and energized from the secondary winding H33 of a transformer Hit. An amplifier and motor control device 28 is connected in circuit with the conductor and controls the operation of the motor H which positions the contact 93 through connections 22. The contact 99 is adapted to be positioned manually. A secondary windin I05 of the transformer tilt is connected to the bridge 95 for energizing the latter.

It will be seen that the potentiometers I00, llll with their adjustable contacts 98, 99 form a bridge circuit, and the output voltage of this circuit opposes the output voltage of the bridge 95 to determine the flow of current through the ampliher and motor control device 20. An unbalance of the output voltages results in an operation of the motor 2| to position the contact 98 until the opposing voltages are equal. An adjustment then of the contact Ssuresults in a change in the. positions ofcontact 98 to produce a balance for predetermined conditions to be measured. The positions of contact 98 are representative'of the conditions. measured, and a changing of these positions by adjustment of contact 99 merely results in an indication of the values from a different zero point. It will be noted that this arrangement makes it possible to read the values as they change in either direction from the zero point since the voltage output of the two bridge circuits are always in opposition to each other.

As a result of my invention there are provided improved systems for measuring a variable or some function of a plurality of variables. In each system there is provided one or more balanceable networks whichareunbalanced on variations of a condition and produce a voltage to be measured. The measurement of the voltage is accomplished in each case by regulating an opposing voltage until it is equal to the voltage to be measured. Although some of the systems have been shown and described as indicating functions of certain variables, it will be understood that they may be applied as well to the indica tion of functions of other variables.

While there are shown in this application several forms which my invention may assume in practice, it will be understood that these forms of the same are shown for purposes of illustration and my invention may be modified and em bodied in various other forms without departing from its spirit or scope of the appended claims.

This application forms a division of my copending parent application S. N. 765,760 filed in the United States August 2, 1947, now Patent No. 2,612,628, issued September 30', 1952.

What I claim as new, and desire to secure by Letters Patent of the United States, is:

1. A measuring system comprising, in combination, a plurality of balanceable networks each adapted to be unbalanced in response to changes in a condition, means for energizing said networks from a common source of alternating current, output connections for said networks across which voltages are produced in proportion to their unbalance, means including a potentiometer energized from said source of alternating current, means for subjecting the output voltages of said networks in opposition to variable portions of the voltage drop across said potentiometer, and

means operable in response. to the difference between said opposed voltages for varying the portion of the voltage drop taken from said po-- tentiometer.

2. A measuring system comprising, in combination, a pair of bridge circuits each having an element forming one of its legs and varying in re.-

sistance in response to changes in a condition,v means for energizing said bridge circuits from a.

common source of alternating current, means for connecting the output voltages of said bridge circuits in opposition to each other, and means re-- sponsive to the diflerences between said output voltages for varying the voltage ,at which one of said bridge circuits is energized.

3. A measuring system comprising, in combination, a pair of bridge circuits each having an element forming one ofits legs and varying in re,- sistance in response to changes in a condition, means including. a pair'of transformers for energizing said bridge circuits from a common source of alternating current, means for connecting the output voltages of said bridge circuits in opposition to. each other, a core member movablerrelative tothewindings clone of said transformers; for varying the. voltage. at which onerof said-bridge circuits is energized, and means responsive to the difference between said bridge output voltages for moving said core member.

4; A measuring system comprising, in combination; a bridge circuit adapted to be unbalanced in response tochanges in a variable condition, a second: bridge circuit having a pair of movable contacts for varying its unbalance, one of. said contacts'being arranged for manual movement, meansincluding a transformerafor, energizing saidrbridgezcircuits from a common source of alternatingcurrent, meansv for. connecting the output voltages of "said bridge circuits in opposition to each other, and means responsive to the difference between saidoutput voltagesfor moving'the other of said movable contacts.

5. A' measuring system including, in combination; a'Wheatstone bridge having an element forming one of its legs and varying in resistance in response to changes in a. first condition; means for. energizing the bridgeat diagonally opposite points'by an alternating current potential; outputsconnections for'the bridge at points between thediagonal points of energization and including inserieswith the. points a voltage magnitude andphase sensitive device, a Wheatstone bridge sensitive tosa second condition, and a source of adjustable: alternating current potential; and

means .controll'edby the sensitive device for ad justing the source of -alternating current potentialuntila balance'is reached between the output of'the bridge and the adjusted A.-C. potential.

6. A measuring system including in combination, a pair. of bridge circuits each having an element forming one of its'legs and varying in resistance in response "to changes in a condition, means. including a pair of movable coretransformers for variably energizing said bridge circuits,core means of first said movable core transformerpositioned in accordance with a condition,

meansfor connecting the outputvoltages of said bridge circuits in opposition to each other, and means-responsive to the -difference between said output voltages for moving the core member of said second movable core-transformer.

7. A fiuid flow compensating system including in combination, a first bridge circuit having an element formingone'of its legs varying in resistance-in accordance with changes in pressure, a=second bridge circuithaving an element formingone offits legs varying in resistance in accordance with changes in temperature, means including apair of movable core transformers for variably energizing said bridge circuits, core means of the firstof said pair of movable core transformers positioned in-accordance with rate of flow, means for connecting the output voltages of said bridge circuitsinopposition to each other, and means responsiveto the difference between said bridge output voltages for moving ,the core of said second movable core transformer, whereby the value of the flow is indicated as having been compensated for temperature and pressure.

References Cited in the file of'this patent UNITED STATES PATENTS Number Name Date 2,495,844 Hornfeck Jan. 31, 1950 2,501,583 Schafer Mar. 21, 1950 2,510,467 Fuge June 6, 1950 2,565,922 Howard Aug; 28, 1951 2,589,597 Beak Mar. 18,1952 

